Influence of the voltage contacts on the four-terminal quantized Hall resistance in the nonlinear regime

The influence of the contacts on the value of the quantized Hall resistance has been studied in a series of high-precision measurements. Deviations of the Hall resistance of up to 0.35 /spl mu//spl Omega///spl Omega/ from the expected value were observed in a device in which the resistance of one of the voltage contacts used in the measurement was comparable to the Hall resistance. The edge-state theory of contacts gives no satisfactory estimate for the observed deviations.